It is well known that a conventional damper utilizes the turbulence of the oil it contains to absorb the shock imparted by an external force. Such turbulence occurs when the oil passes through narrow slits provided within the damper as oil is pressed by the external force.
However, with such a damper, high precision is required for the make of the slits to accurately generate a required resisting force in order to accurately produce the required damping effect. Morever, as oil cannot be compressed when a strong external force is abruptly applied to it, the external force is apt to be directly received by the strucural members the damper is supposed to protect. To overcome this problem, a damper is normally designed to have an excessively high strength against external force, making in turn its overall size very bulky. Besides, the slits are liable to become narrow as dust and other foreign matters are caught by the slits and eventually clogged to completely block the flow of oil.
In order to eliminate these disadvantages of the damper of the conventional designa as described above, an improved damper has been proposed, which basically comprises two independent solid members arranged in such a manner that they are movable relative to each other and have surfaces located vis-a-vis and close to each other and a highly viscous liquid material filled therebetween so that it can provide resistance against external force due to the viscous drag of the liquid material against shearing force that can be generated without raising the internal pressure of the liquid when an external force is applied thereto.
A typical damper which was realized in relatively early days on the basis of this design a concept comprises a casing in which a certain number of movable discs are radially and perpendicularly fitted to a rotary shaft and a same number of fixed discs are fitted to the casing in such a manner that the movable discs and the fixed discs are arranged alternatively with an appropriate clearance between any two adjacent discs and the oil which is contained within the casing fills the spaces between the discs.
With a damper having a configuration as described above, when an external force is applied to the rotary shaft, the movable discs fitted thereto and the fixed discs fitted to the casing are caused to move relative to each other and the viscous liquid filling the spaces between the discs generates viscous drag against the shearing action of the external force to bring forth the overall effect of the damper. However, with such an arrangement, the distance between the two adjacent discs has to be precisely identical for all the discs. If not, the portion of the viscous fluid found between a pair of discs having a relatively small clearance generates a larger viscous drag than the portion of the fluid found between a pair having a relatively large clearance, causing an unreasonably large stress to occur in the are having a large viscous drag that can eventually damage the damper, since the discs are rigidly fitted either to the casing or the rotry shaft and the clearance between a pair of adjacent discs and are not adjustable.
Consequently, manufacture of such a damper requires a considerable high precision. Moreove, such a damper is not capable of altering its damping effect by altering the surface area of the discs because they are rigidly fitted to the supporting members and not accessible from outside, while the amount of viscous drag is proportional to the surface area of the adjacent discs which are facing to each other. This means that if a damper having a different damping effect is needed, a completely new damper has to be provided.
In order to eliminate the drawbacks of the above described damper of the early days, a rotational damper using a plurality of discs and a viscous fluid material has been proposed (Japanese Utility Publication No. 57-39664). FIGS. 22a and 22b illustrate a damper according to the disclosed utility design.
This damper comprises, as in the case of the above described damper of the early days, cylindrical casing a having rotatable shaft c along its longitudinal axis which is rotated when an external force is applied to a pivotable arm b fitted to said rotatable shaft c. A plurality of movable discs d, d, . . . are arranged radially and perpendicularly to said rotary shaft c and rigidly fitted thereto by welding or some other means, while a plurality of fixed discs e, e, . . . are fitted to casing a not rigidly but through engagement of grooves f, f, . . . of said fixed discs e, e, . . . and a pair of longitudinal ridges g, g so that while fixed discs e, e, . . . are blocked against rotating movement, they can be deflected in the axial direction of the damper within a certain limit as most clearly seen in FIG. 22(a). The space within casing a is filled with viscous fluid as in the case of the damper described earlier.
This improved damper is advantageous in that it is free from any damage if an unreasonable force is applied from outside to fixed discs e, e, . . . in the axial direction, because said fixed disc e, e, . . . are so arranged that they can be axially deflected and thereby absorb the external force and that even when there is a fixed disc e which is located significantly closer to one of its adjacent movable discs than to the other and hence generates a viscous drag against shearing force relatively larger than the viscous drage generated between disc e and the other adjacent movable disc as movable discs d, d, . . . are rotatingly moved relative to fixed discs e, e, . . . , said fixed disc e is automatically pushed away to come closer to the other adjacent movable disc having a relatively small viscous drag between itself and said fixed disc e. By this action (so-called alignment effect), each of fixed discs e, e, . . . always tends to take a position where it evenly divides the space between two neighboring movable discs to generate a viscous drag which is equal to those generated by the rest of the fixed discs, thereby preventing any possible damages from occuring due to abnormally large viscous drags that are loacally generated.
However, this improved damper also has certain drawbacks. Firstly, since movable discs d, d, . . . are rigidly fitted to rotary shaft c, they are required to be located with high precision to ensure an evenly distributed viscous drag. Secondly, since the distance between any adjacent movable disc is not adjustable, the surface area of each fixed disc e needs to be altered, if the magnitude of the overall viscous drag is required to be changed.
Therefore, alteration of the surface area of fixed disc e, e, . . . is practically not feasible because such an operation requires dismantling of the damper assembly and disengagement as well as reengagement of the fixed discs with axial ridges g, g. A completely different damper should be provided to realize a viscous drag which is different from that of the original damper.
Moreover, since movable discs d, d, . . . are rigidly fitted to rotary shaft c, alteration of the distance between any given movable disc d and the adjacent disc e from outside is practically not feasible although such capability of alteration is indispensable for a damper that can meet the practically requirement of adjusting its viscous drag within a certain limit.
Consequently, if a variable damping effect is required for a given application, there have to be prepared a number of dampers having different damping effects that satisfy the requirements by providing casings, movable discs and fixed discs with different sizes. With such an arrangement, a damper having a large clearance between the adjacent movable fixed discs or one having a relatively small surface area of the movable and fixed discs may be used if a small damping effect is required, whereas a damper having a small clearance between the adjacent movable and fixed discs or one having a relatively large surface area of the movable and fixed discs may be used for a relatively small viscous drag.
A damper of the type as described above is also accompanied by another major drawback. Any viscous fluid material contained in the damper loses its vicosity and hence its viscous drag against shearing force to some extent as the ambient air temperature rises in summer, whereas it obtains an additional viscosity and hence an additional viscous drag to certain extent in winter when the temperature falls. So, a damper that operates normally in winter can have a poor damping effect in summer and, if it is used as a door check, come to be a defective device that can not effectively absorb shocks and allow the door to bang when it is shut.
It is therefore an object (the first object) of the present invention to provide a damper which is designed on the basis of a completely new concept of using fixed discs and movable discs that can be axially deflected, a concept which is totally different from that of the above described conventional dampers comprising both fixed and movable discs respectively rigidly fitted to a casing and a rotary shaft or axially deflectable fixed discs fitted to a casing and movable discs rigidly fitted to a rotary shaft, where rigidly fitted members are involved in any case. According to this new concept, not only the fixed disc but also the movable discs are so arranged that they can be axially deflected. Thus, when the movable discs are subjected to an external force in the form of rotation or traction so that they come to form clearances with their adjacent fixed discs having distances which are different from one another, a flow of the viscous fluid occurs within the damper to bring forth the above-mentioned alignment effect (an effect of viscous fluid to flow from areas where the viscous drag is low to areas where the drag is high, or areas where the clearance of adjacent discs is narrowed, to equalize the clearances) and equalize the clearance for all the discs. With such an arrangment, a damper which is free from damage due to abnormally high local viscous drags can be manufactured without requiring high precision.
It is another object (the second object) of the present invention to provide a damper comprising deflectable fixed and movable discs as described above by referring to the first object, said damper further having an axial total effective length that can be adjusted from outside within a predetermined limit to alter the clearance of the adjacent discs and hence the overall damping effect of the damper rapidly and easily.
It is a further object (the third object) of the present invention to provide a damper as described above by referring to the second object, said damper further comprising resilient members capable of restoring the axial total effective length of the damper when it is axially compressed to ensure a smooth initial action of the damper and an easy adjustment of its effects.
It is a still further object (the fourth object) of the present invention to provide a damper, unlike dampers as described above by referring to the second and third objects and having a means for adjusting the viscous drag, comprising a means for altering the number of movable discs which are rotated with a rotary shaft through an operation conducted from outside to adjust the overall drag of the damper and a means for replacing all the replaceable fixed and movable discs with those having a different surface area easily and rapidly to alter the nominal viscous drag of the damper.
It is a still further object (the fifth object) to provide a damper comprising axially deflectable fixed and movable discs whose clearances can be easily altered simply by altering the axial total effective length of the damper from outside to adjust the overall drag of the damper and a means for replacing the replaceable fixed and movable discs with those having a different surface area to alter the nominal drag of the damper, said damper further comprising a deformable feeler element sensitive to temperature change within the casing at a location where said element is effectively thermally deformed to automatically maintain the predetermined level of drag of the damper regardless of temperature change without necessity of adjustment by operators.
It is a still further object (the sixth object) of the present invention to provide a damper, unlike the one having a feeler element as described above by referring to the fifth object, comprising movable discs and fixed discs either or both of which are made of a thermally deformable material which is sensitive to temperature change to effectively utilize the thermal deformation of the discs made of such a material to maintain the predetermined level of drag of the damper regardless of temperature change without necessity of adjustment by operators.
It is a still further object (the seventh object), of the present invention to provide a damper comprising, is addition to the features of the one as described by referring to the fourth object, movable and fixed discs constantly under the effect of a resilient external force, either or both of said movable and fixed disc being made of a thermally sensitive and deformable bimetal to effectively utilize thermal deformation of the bimetal to maintain the predetermined level of drag of the damper, regardless of temperature change without necessity of adjustment by operators.